/Engine/Source/Editor/AssetDefinition/Public/AssetDefinitionRegistry.h
NormallyUAssetDefinitionRegistryare registered automatically by their CDO. The only reason you need to do this is if you're forced to dynamically create theUAssetDefinitionat runtime. The original reason for this function was to be able to create wrappers for the to be replacedIAssetTypeActions, that you can access AssetDefinition versions of any IAssetType making the upgrade easier.
void RegisterAssetDefinition ( [UAssetDefinition](API\Editor\AssetDefinition\UAssetDefinition) * AssetDefinition )